By law, currently all off-road and on-road diesel must be Ultra Low Sulfur. Currently the law says the highway past my place has a 55 mph limit but probably half the drivers break that law. The other half are intoxicated or on drugs and don't know. So it follows that some suppliers are ignoring the law (know a way to avoid detection) and are supplying inferior fuel. It also follows that if they have inferior fuel, they stand less of a chance getting caught selling it to off-road users than selling it to on-highway users where there are checks not only whether the driver is using dyed fuel but also the fuel meets specs. Having had enormous amounts of warranty failure data to examine and reports that I could read regarding the failed pumps, I could pick out some areas of the USA that have the worst fuel in the world based on fuel pump failure analysis. I am talking about 10 times failure rate differences.